1. Technical Field of the Invention
The present invention relates to a liquid container of an atmosphere communication type which is suitable as an ink cartridge to be attached to an ink jet printer, for example.
2. Description of the Related Art
As an ink cartridge (a liquid container) to be attached to an ink jet printer, there have variously been proposed an atmosphere communication type comprising, in a container body to be attached to the printer, an ink containing portion (a liquid containing portion) for accommodating an ink, an ink supply portion (a liquid supply portion) to be connected to a print head (a liquid ejection portion) on the printer side, an ink leading path (a liquid leading path) for leading the ink stored in the ink containing portion to the ink supply portion, and an atmosphere communication port for introducing atmosphere from an outside into the ink containing portion with a consumption of the ink in the ink containing portion.
Moreover, some ink cartridges are provided with an ink residual amount detecting mechanism in which a sensor having a piezoelectric oscillator is disposed at a reference height in the liquid containing portion (for example, see JP-A-2001-328278).
The ink residual amount detecting mechanism serves to detect that the liquid level of the ink is reduced to the reference height based on a change in an oscillating characteristic (a residual oscillation) in the case in which a periphery of the sensor is filled with a ink liquid and the case in which atmosphere comes in contact with the periphery of the sensor when the ink liquid level of the liquid containing portion is reduced to the reference height due to the consumption of the ink by a print processing so that the outside atmosphere introduced into the liquid containing portion through an atmosphere communication port reaches a detecting position of the sensor with the consumption of the ink. A detection signal is utilized for a display of the residual amount of the ink or a notice of a time for exchange of the cartridge.
In the ink cartridge of the atmosphere communication type, the outside atmosphere introduced into the liquid containing portion through the atmosphere communication port with the consumption of the ink is changed into fine air bubbles due to a shock acting in the attachment and removal of the cartridge and floats in the ink liquid in some cases. When the air bubbles floating in the ink liquid are stuck to a surface of the sensor, the air bubbles thus stuck causes a change in a residual oscillation so that the presence of the ink cannot be detected accurately. Consequently, there is a possibility that it might be erroneously detected that the liquid level of the ink is reduced.
In order to prevent the erroneous detection, therefore, there has been known a technique for surrounding the sensor by a partition wall with a fine gap to permit a pass of the ink left and for preventing an intrusion of the air bubbles into the sensor side by a capillary force of a meniscus generated in the gap when the air bubbles reach the gap formed by the partition wall, thereby preventing the erroneous detection (for example, see JP-A-2004-195653, hereinafter referred to as 'JP-A-653).
In order to accurately give a notice of the time for exchange of the cartridge in use of a printer, it is effective that a sensor for detecting the presence of an ink is provided in the vicinity of a liquid supply portion to be an outlet of the ink to the printer side in order to quickly detect the fact that a residual amount of the ink in the liquid containing portion is zero.
Even if the sensor is provided in the vicinity of the liquid supply portion, however, the air bubbles mixed into the ink are stuck to the sensor and it is thus detected erroneously that the residual amount of the liquid in the liquid containing portion is zero in some cases.
It can be proposed that the sensor is provided in the vicinity of the liquid supply portion and a technique described in 'JP-A-653 (a technique for preventing a passage of air bubbles utilizing a meniscus) is applied in order to prevent the air bubbles in the ink from reaching the sensor side.
In the technique described in 'JP-A-653, however, in the case in which a cartridge removed from a printer is vibrated strongly or a strong shock is applied due to a drop in a situation in which a cartridge which is being used for changing a color is removed from the printer and is stored, for example, there is a possibility that the air bubbles might flow into the sensor side beyond a capillary force generated by a meniscus. Therefore, a reliability for preventing the erroneous detection is low.
For example, in some cases in which the liquid container is used in a cold district, the liquid freezes and expands, and goes out of an atmosphere communication port which is opened to the atmosphere. When the liquid container is returned into a normal temperature environment and the freezing liquid liquefies again, the atmosphere on the outside is drawn into the liquid containing portion through the atmosphere communication port. Also in this case, there is a possibility that air bubbles might be generated in the liquid to cause the erroneous detection of the sensor.